1. Field of the Invention
The present invention relates to a control apparatus for a hybrid vehicle which can optimize energy management when the vehicle is driving at a high speed.
2. Description of the Related Art
Conventionally, hybrid vehicles are well-known which have electric motors as power sources for driving the vehicles in addition to engines.
In conventional hybrid vehicles, there are parallel hybrid vehicles which use motors as assisting driving sources for assisting the output from the engines. Parallel hybrid vehicles assist the output from the engine by the motor when the vehicle accelerates, charge the battery by deceleration regeneration when the vehicle decelerates, and perform various controls, to respond the driver""s demands while maintaining the remaining charge (electric energy) of the battery (as disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 7-123509).
When a conventional hybrid vehicle is accelerating, the motor assists the output from the engine. The assistance of the output from the engine by the motor is maintained even when the vehicle is driving at a high speed when the fuel supply to the engine is stopped by a limiter. In this case, even though the engine is controlled to decelerate the vehicle, the motor is controlled to assist the driving power from the engine, thus causing inconsistencies in the controls.
The unnecessary assistance by the motor decreases the remaining charge of the battery, causing problems in energy management.
For example, the vehicle drives at a high speed while stopping the fuel supply, the vehicle then decelerates, and the motor enters a deceleration mode to perform regeneration. In this case, the deceleration may be excessive, and the driver may experience a feeling of unease.
It is therefore an object of the present invention to provide a control apparatus for a hybrid vehicle which restricts the assistance of the engine by the motor, and which appropriately controls electric generation.
In a first aspect of the present invention, the control apparatus is provided in a hybrid vehicle with a combustion engine (E) for outputting a driving force, an electric motor (M) for generating a force for assisting the output from the engine, depending on the driving conditions, a power storage unit (battery 3) for storing electric energy generated by the motor acting as a generator using the output from the engine and electric energy regenerated by the motor when the vehicle decelerates. The control apparatus includes: a speed limiter (step S100A) for decreasing the driving force produced by the motor when the vehicle speed exceeds a first threshold value (assist trigger look-up upper limit vehicle speed #VMASTHG) while the engine and the motor produce the driving force; a generation starter (step S100B) for starting generation by the motor when the vehicle speed exceeds a second threshold value (the high vehicle speed VASTVHG, shown in FIG. 15, at which the assistance is zero) which is higher than the first threshold value; and a generation amount setting device (step S250) for setting the amount of generation, depending on the driving conditions of the vehicle, when the generation starter starts the generation. The motor generates the electric energy, depending on the amount of generation set by the generation amount setting device.
When the vehicle speed exceeds the first threshold value, the unnecessary driving force is decreased. Further, when the vehicle speed exceeds the second threshold value, the motor starts the generation to restrict the increase of the vehicle speed.
That is, as compared with the case where the fuel supply to the engine is suddenly stopped, the feeling of unease felt by the driver is reduced.
In a second aspect of the present invention, the speed limiter decreases the driving force produced by the motor after the vehicle speed exceeds the first threshold value until the vehicle speed reaches the second threshold value, and makes the motor stop the production of the driving force when at the second threshold value.
When at the second threshold value, the motor stops producing the driving force, and can continuously start the generation.
That is, once the motor stops producing the driving force, the motor smoothly starts the generation, thereby preventing the driver from experiencing the feeling of unease.
In a third aspect of the present invention, the control apparatus includes a fuel supply stopper for repeating stopping of the supply of fuel at a predetermined interval when the vehicle speed reaches a fourth threshold value which is higher than the second threshold value.
The control apparatus can reliably decrease the vehicle speed even the braking by stopping the assistance for the engine while starting the generation by the motor is insufficient.
Therefore, the energy is not unnecessarily consumed when the vehicle is driving at a high speed, thereby reducing the fuel consumption.
In a fourth aspect of the present invention, the generation amount setting device sets the amount of generation, depending on the degree of throttle opening, when the vehicle speed exceeds a third threshold value which is higher than the second threshold value and lower than the fourth threshold value.
When decelerating the vehicle by the generation by the motor, the amount of generation can be adjusted by the generation amount setting device, depending on the degree of the throttle opening indicating the driver""s intention.
Once the motor starts the generation, the amount of generation is set depending on the degree of throttle opening. Therefore, the vehicle decelerates depending on the depression of the accelerator pedal by the driver, and this prevents the driver from experiencing a feeling of unease. As the result, the energy management can be optimized, and the commercial value of the vehicle is increased.